# A Strain-Compensated InGaAs/InGaSb Type-II Superlattice Grown on InAs Substrates for Long-Wavelength Infrared Photodetectors

## TL;DR

Researchers created a new type of infrared detector using a strain-compensated superlattice material, achieving high performance for long-wavelength infrared detection.

## Contribution

The first demonstration of a highly strained InGaAs/InGaSb superlattice on InAs substrates for long-wavelength infrared detection.

## Key findings

- The superlattice structure achieved a 50% cutoff wavelength of approximately 12.1 μm at 77 K.
- Devices showed a dark current density of 7.96 × 10−2 A/cm2 and a peak responsivity of 4.90 A/W at 77 K.
- A peak quantum efficiency of 65% and specific detectivity of 2.74 × 1010 cm·Hz1/2/W were achieved.

## Abstract

In this paper, the first demonstration of a highly strained In0.8Ga0.2As/In0.2Ga0.8Sb type-II superlattice structure grown on InAs substrates by molecular beam epitaxy (MBE) for long-wavelength infrared detection was reported. Novel methodologies were developed to optimize the As and Sb flux growth conditions. The quality of the epitaxial layer was characterized using multiple analytical techniques, including differential interference contrast microscopy, atomic force microscopy, high-resolution X-ray diffraction, and high-resolution transmission electron microscopy. The high-quality superlattice structure, with a total thickness of 1.5 μm, exhibited exceptional surface morphology with a root-mean-square roughness of 0.141 nm over a 5 × 5 μm2 area. Single-element devices with PIN architecture were fabricated and characterized. At 77 K, these devices demonstrated a 50% cutoff wavelength of approximately 12.1 μm. The long-wavelength infrared PIN devices exhibited promising performance metrics, including a dark current density of 7.96 × 10−2 A/cm2 at −50 mV bias and a high peak responsivity of 4.90 A/W under zero bias conditions, both measured at 77 K. Furthermore, the devices achieved a high peak quantum efficiency of 65% and a specific detectivity (D*) of 2.74 × 1010 cm·Hz1/2/W at the peak responsivity wavelength of 10.7 µm. These results demonstrate the viability of this material system for long-wavelength infrared detection applications.